Rotary helical splined actuators have been employed in the past to achieve the advantage of high-torque output from a simple linear piston-and-cylinder drive arrangement. The actuator typically uses a cylindrical body with an elongated rotary output shaft extending coaxially within the body, with an end portion of the shaft providing the drive output. An elongated annular piston sleeve has a sleeve portion splined to cooperate with corresponding splines on a ring gear attached to the sidewall of the body and on the output shaft exterior. The piston sleeve is reciprocally mounted within the body and has a head for the application of fluid pressure to one or the other opposing sides thereof to produce axial movement of the piston sleeve.
As the piston sleeve linearly reciprocates in an axial direction within the body, the outer splines of the sleeve portion engage the splines of the ring gear to cause rotation of the sleeve portion. The resulting linear and rotational movement of the sleeve portion is transmitted through the inner splines of the sleeve portion to the splines of the shaft to cause the shaft to rotate. Bearings are typically supplied to rotatably support one or both ends of the shaft relative to the body.
A shortcoming of such rotary helical actuators, however, is that the attachment of the ring gear to the body is typically accomplished by pins which each extend through one of a plurality of circumferentially distributed through bore holes in the body sidewall and into a corresponding one of a plurality of circumferentially distributed bore holes in the ring gear. The heads of the pins are then welded to the body sidewall to hold them firmly in position and to prevent fluid leaks. This approach allows the splines of the ring gear to be machined before the ring gear is installed in the body. However, several manufacturing steps are required to form the bore holes in the ring gear and the through bore holes in the body sidewall, install the pins and weld the pin heads to the body sidewall. Not only does this make the manufacture of the actuator more complicated, time-consuming and expensive, but the through bore holes in the body sidewall weakens the body sidewall and presents the possibility of a fluid leak during fluid-powered operation.
Although it is possible to avoid the use of through bore holes in the body by machining the splines directly on the interior surface of the body sidewall, doing so is difficult, time-consuming, and expensive. In part, this is because the splines must be cut on an interior surface of the body along its midportion at a distance from the body ends.
It will therefore be appreciated that there has long been a significant need for a fluid-powered rotary actuator with a ring gear fixedly attached to the body without the use of pins and through bore holes in the body sidewall. The ring gear should be simple and quick to install, eliminate the possibility of fluid leakage during operation and not weaken the body sidewall so as to reduce manufacturing cost and increase reliability. The present invention fulfills these needs and further provides other related advantages.